Why SIMOS 18 ECUs Fail on the Old CGFC 200 Harness
The new CG FC200 DAP tool supports the ECU, but programming fails during identification, reading, or writing.
The problem is often not the tool or the software, but the CGFC 200 harness wiring—specifically, missing GPT communication lines.
Understanding the Difference Between 2 GPT and 4 GPT Wiring
Older CG FC100 and early CG FC200 adapter harnesses were designed with only two GPT lines.
This configuration worked perfectly for older ECU generations.
However, Bosch SIMOS 18 ECUs and newly updated control modules require four GPT lines for stable communication.
The newer DB15 harness includes:
- GPT0
- GPT1
- GPT2
- GPT3
Those extra GPT2 and GPT3 lines are essential, not optional.
Why the DB15 Harness Works with SIMOS 18 ECUs
The DB15 harness adds the missing data channels needed by modern ECUs.
Without these channels:
- The tool may connect
- ECU identification may fail
- Read or write operations may stop unexpectedly
This is why many Simos 18 ECUs appear “unsupported” on older CG FC harnesses, even though the tool itself is fully capable.
Two Solutions for CG FC200 Users
Technicians currently have two practical options:
Option 1: Buy the Official DB15 Harness
Plug and play
No wiring risk
Higher cost
Option 2: Modify the Existing CGFC 200 Harness
Lower cost
Requires wiring knowledge
Must be done correctly
Correct GPT Pin Information for DB15 Harness
If you choose to modify your harness, the verified and correct pin assignments are:
1. Pin 7 → GPT2 → Pink wire
2. Pin 11 → GPT3 → Blue wire
These two GPT lines are missing from older harness designs.
When adding the wires:
- Ensure correct polarity
- Verify continuity
- Use proper insulation
- Double-check PINs
One loose or incorrect connection can damage the ECU.
Why Wiring Matters More Than Software
Many technicians blame software updates when programming fails.
In reality, wiring limitations are responsible for a large percentage of these issues.
Once GPT2 and GPT3 are added correctly, a modified FC200 DAP adapter harness can functionally match the DB15 harness for supported SIMOS 18 ECUs.